1. Field of the Invention
This invention relates to methods and apparatus for performing minimally invasive surgery, and more particularly to instruments for protecting body structures in a patient.
2. Background Information
Spinal surgery presents significant difficulties to the surgeon attempting to reduce chronic back pain or correct spinal deformities without introducing additional trauma due to the surgical procedure itself. In order to access the vertebrae to perform spinal fixation, discectomy or related procedures, the surgeon is typically required to make large incisions and cut or strip muscle tissue surrounding the spine. During these procedures, care must be taken not to injure nerve tissue in the area.
Apparatus for performing minimally invasive techniques have been proposed to reduce the trauma of posterior spinal surgery by reducing the size of the incision and the degree of muscle stripping in order to access the vertebrae. U.S. Pat. No. 6,187,000 to Davison et al., entitled “Cannula for Receiving Surgical Instruments,” discloses a novel cannula or retractor which receives surgical instruments for performing a surgical procedure on a body. The cannula or retractor includes an expandable portion for enabling an increase in the cross-sectional area of the passage at the distal end. The expandable portion of the tube structure, when expanded, provides an enlarged operative space.
Such minimally invasive techniques provide significant advantages in terms of reduced blood loss and trauma. The '000 patent describes a novel device which provides improved access over prior art cannulas. Nevertheless, any minimally invasive procedure provides diminished access when compared with traditional open procedures. The presence of delicate nerve tissue in the spinal region, especially when interbody fusion procedures are being performed, requires extra care on the part of the surgeon to avoid damaging such tissues.
U.S. Pat. Nos. 6,425,859 and 6,007,487 to Foley et al. describe a retractor for manipulating through tissue. The retractor provides no mechanism for releasably mounting the retractor with respect to a cannula, so that the retractor can be released and removed from the cannula without disturbing the cannula, or other instrumentation positioned therein. Moreover, the primary function of the device described in the 859 and 487 patents is retraction of tissues rather than protection of the nerve and dura.
Accordingly, there is a need in the art for an apparatus and a method of surgery to protect such body tissues, while still affording good visibility, and which is easily positionable.